Field of the Invention
The present invention relates to a method for generating a prediction block of an image that has been encoded in Advanced Motion Vector Prediction (AMVP) mode, and more particularly, to a method for decoding motion information encoded in AMVP mode and generating a prediction block based on the motion information.
Discussion of the Related Art
Many techniques have been proposed to effectively compress a video signal with a video quality maintained. Particularly, inter-prediction coding is one of the most effective video compression techniques, in which a block similar to a current block is extracted from a previous picture and the difference between the current block and the extracted block is encoded.
However, motion information about each block should be additionally transmitted in the inter-prediction coding scheme, with a coded residual block. Therefore, effective coding of motion information that reduces the amount of data is another video compression technique.
In motion estimation coding, a block best matching to a current block is searched in a predetermined search range of a reference picture using a predetermined evaluation function. Once the best matching block is searched in the reference picture, only the residue between the current block and the best matching block is transmitted, thereby increasing a data compression rate.
To decode the current block when coded through motion estimation, information about a motion vector representing a difference between a position of the current block and that of the best matching block is needed. Thus, the motion vector information is encoded and inserted into a bit stream during coding. If the motion vector information is simply encoded and inserted, overhead is increased, thereby decreasing the compression rate of video data.
Accordingly, the motion vector of the current block is predicted using neighboring blocks and only the difference between a motion vector predictor resulting from the prediction and the original motion vector is encoded and transmitted, thereby compressing the motion vector information in the inter-prediction coding scheme.
In H.264, the motion vector predictor of the current block is determined to be a median value (mvA, mvB, mvC). Since the neighboring blocks are likely to be similar to one another, the median value of the motion vectors of the neighboring blocks is determined to be the motion vector of the current block.
However, if one or more of the motion vectors of the neighboring blocks are different from the motion vector of the current block, the median value does not predict the motion vector of the current block effectively.
In addition, as prediction blocks are larger in size and diversified, the number of reference pictures is increased. Thus, the data amount of a residual block is reduced but the amount of motion information to be transmitted (a motion vector and a reference picture index) is increased.
Accordingly, there exists a need for a technique for more effectively reducing the amount of motion information to be transmitted. In addition, a technique for efficiently reconstructing motion information encoded in the above technique is needed.